Regenerative radio receiver



Aug. 29, 1939. P. H. K. G. CORNELIUS 2,171,139

REGENERATIVE RADIO RECEIVER Filed April 21, 1957 INVENTOR R H- ICQ- CORNELI US BY K fm ATTORNEY Patented Aug. 29, 1939 UNITED STATES PATENTOFFIE lands, assignor to N.

V. Philips Gloeilampenfabrieken, Eindhoven, Netherlands, a corporationof the Netherlands Application April 21, 1937, Serial No. 138,132 In theNetherlands June 29, 1936 6 Claims.

This invention relates to a back-coupled receiving circuit arrangementand more particularly to a radio-receiving arrangement in which eithergridor diode-detection is used and in which the detector is connected inparallel to an oscillatory circuit which is undamped by backcoupling.

Such receiving arrangements have the drawback that the degree'Ofback-coupling at which the circuit arrangement commences to oscillatewith increasing back-coupling is higher than the value at which it stopsoscillating with decreasing back-coupling. More particularly whenreceiving signals from remote transmitters it is desirable that theback-coupling should be adjusted so that the circuit arrangement justfails to oscillate. This adjustment is greatly impeded by the phenomenonreferred to above. Indeed, when the back-coupling is too strong, so thatincreases. In fact, the diode or the grid-cathode impedance of thegrid-detector constitutes a resistance which is connected in parallel tothe oscillatory circuit and whose value is small (of the order ofmagnitude of 25,000 ohms) with small amplitudes of the oscillationssupplied to the detector, whilst with increasing amplitudes thisresistance increases up to -a value corresponding to about half theleakage resistance of the detector (for example, of the order ofmagnitude of 250,000 ohms). When the circuit arrangement does notoscillate, the amplitude of the oscillations supplied to the detector issmall when receiving a remote transmitting station, so that theoscillatory circuit is strongly damped and strong back-coupling must beused to cause the arrangement to oscillate. As soon as it startsoscillating the amplitude of the oscillations supplied to the detectormaterially increases due to which the damping of the oscillatory circuitdecreases and the back-coupling must be appreciably reduced to stopself-oscillation.

According to the invention the detector is negatively biased to such adegree that the damping of the oscillatory circuit caused by thedetector increases or remains approximately constant with thearrangement oscillates, then the back-couincreasing amplitudes of theoscillations supplied to the detector.

When thedetector is negatively biased to such a degree that the anodecurrent of the diode or the grid-current of the grid-detector is cut ofiin the absence of oscillations, then the damping of the oscillatorycircuit caused by the detector will be zero with small amplitudes, thusobtaining at any rate an increase of the damping with increasingamplitudes. However, this Will involve a certain amount of distortionand for this reason it is not desirable that the negative bias should begiven such a high value. In the commonly used diodes the correct valueof the negative bias at which a substantially constant or a slightlyincreasing damping is achieved with increasing amplitude lies aboutbetween 0.5 and and 0.8 volt, the extreme limits being about 0.2 and 1.3volts.

The invention will be more clearly understood by reference to theaccompanying drawing the single figure of which represents, by way ofexample, one form of construction thereof.

This drawing shows part of a radio-receiving circuit arrangement. Theoscillations intercepted by the antenna 1 are supplied to the controlgrid 20 of the amplifying tube 3 through the coupling element 2 whichmay comprise, if desired, one or more amplification stages and/or afrequency-' transformation stage. The cathode circuit of said tubecomprises a resistance 4 which is shunted by a condenser 5 and serves toproduce a suitable bias on grid 20. The anode circuit of the amplifyingtube 3 comprises a tuned oscillatory circuit consisting of an inductancecoil 6 and a condenser i. The coil 6 is coupled with a backcoupling coil8, whilst the voltage set up in the back-coupling coil is supplied tothe control grid 20 of the tube 3 through a variable condenser 9. Theoscillations occurring in the circuit 6, l are supplied through acondenser 10 to a detector H which is represented here as a diode havingan anode 2i and cathode 22. Instead of a diode it is also possible touse a grid-detector. The output circuit of the diode comprises a chokecoil 12 toprevent the condenser l3 from being connected in parallel tothe circuit 6, I. The audio frequency voltage occurring across theresistance 14 is supplied through the condenser 15 to an audio frequencyamplifier (not shown). According to the invention the direct currentcircuit of the diode comprises a source of potential 16 the positiveterminal of which is connected to the cathode 22, whereas its negativeterminal is connected to the anode 2| so that the diode receives anegative bias of about 0.5 to 0.8 volt. The source of potential i6 isrepresented as a battery, but it may have any other suitable form. Forexample, the direct current circuit of the diode may comprise aresistance which is traversed by the anode current of one of theamplifying tubes of the receiver.

In the circuit arrangement represented in the drawing the diode itserves for demodulation of V the incoming oscillations. However it willbe appreciated that the invention also includes circuit arrangements inwhich a diodeor grid-detector is connected in parallel to a circuitundamped by back-coupling, said detector serving to produce a controlvoltage, for instance, for automatic volume control.

Having described my invention, what I claim as novel and desire tosecure by Letters Patent is:

1. In a device of the class described, the combination of a parallelresonant circuit tunable to a desired signal frequency, a detectorhaving a cold electrode and a heated cathode, means connecting saiddetector electrodes in parallel across said resonant circuit and meansfor maintaining said cold electrode at a potential which is negativewith reference to that of said heated cathode by such an amount thatsaid detector has no damping action on said resonant circuit for smallvariations of voltage across said detector electrodes.

2. In a device of the class described, the combination of a parallelresonant circuit tunable to a desired signal frequency, a detectorhaving at least two electrodes comprising a cold electrode and a heatedcathode, means connecting said detector electrodes in parallel acrossthe ends of said resonant circuit and a circuit conductive to directcurrrent connected between said detector electrodes and including asource of steady potential having a value between 0.2 volt and 1.3volts, the positive terminal of said potential source being connected tosaid detector cathode.

3. In a device of the class described, the combination of a parallelresonant circuit tunable to a desired signal frequency, a detectorhaving a cold electrode and a heated cathode, a condenser having oneside connected to said cold electrode and its other side to one terminalof said resonant circuit, a circuit conductive to direct currentconnected between the other terminal of said resonant circuit and saidheated cathode and means for maintaining said cold electrode at anaverage negative potential with reference to said heated cathode.

4- Means for receiving radio frequency signal currents comprising incombination, a parallel resonant circuit tunable to the frequency of thesignal currents, a diode detector having an anode and heated cathode, acondenser having one side connected to said anode and its other side toone terminal of said resonant circuit, a connection between the otherterminal of said resonant circuit and said heated cathode, and a circuitconductive to direct current connected between said anode and cathodeand including the series connection of a choke coil, a resistor and asource of negative potential.

5. In radio receiving apparatus including means to connect the apparatusto a source of signal energy and a detector tube and wherein means areprovided including a resonant circuit for connecting the first namedmeans to said detector tube, said detector tube having an anode and acathode, an input for said detector including means for connecting saiddetector electrodes in parallel across said resonant circuit and meansfor maintaining the anode of said detector at a potential which isnegative with reference to that of the cathode thereof to such a degreethat the damping of the said resonant circuit caused by the detectorincreases with increasing amplitudes of signal voltage applied to thedetector input.

6. The circuit arrangement described in the next preceding claim furthercharacterized by that the detector tube anode is maintained at anegative potential of the order of 1 volt with respect to the cathode.

PETER H. K. G. CORNELIUS.

